Sensor and method for the manufacture

ABSTRACT

A sensor, in particular for determining the oxygen content in exhaust gases of internal combustion engines, is proposed, as well as a method for its manufacture. The sensor includes a receptacle, arranged in a longitudinal bore ( 16 ) of a metal housing ( 10 ), for a sensing element ( 12 ), in which receptacle the sensing element ( 12 ) is received in gas-tight fashion via a sensing element seal, the sensing element seal being a glass seal ( 57 ). The receptacle has a measured-gas-side ceramic shaped element ( 20 ) and a connector-side ceramic shaped element ( 27 ), which are arranged axially one behind the other. A cavity ( 55 ) into which the glass seal ( 57 ) is pressed while hot is configured between the two ceramic shaped element ( 20, 27 ).

BACKGROUND INFORMATION

[0001] The invention proceeds from a sensor according to the species defined in the principal claim. A sensor of this kind is known from U.S. Pat. No. 5,467,636, in which a planar sensing element is immobilized in gas-tight fashion, by way of a sealing element, in a passthrough of an exhaust-gas-side lower ceramic shaped element. The exhaust-gas-side ceramic shaped element has on the end surface facing away from the exhaust gas a recess which surrounds the passthrough and into which a glass seal is introduced. A further ceramic shaped element, which is joined via a metal solder join to the housing, sits on the glass seal. The glass seal encloses the sensing element inside the recess, and constitutes a gas-tight join between ceramic shaped element and sensing element at this point.

SUMMARY OF THE INVENTION

[0002] The sensor according to the present invention, having the characterizing features of the principal claim, has the advantage that a mechanically stable and gas-tight join is possible between the planar sensing element and both ceramic shaped elements.

[0003] The hermetic seal of the sensing element thereby achieved is vibration-proof, so that while the sensor is being used in the motor vehicle, the sensing element can be immobilized over the utilization period in mechanically stable and hermetic fashion. The method according to the present invention makes it possible for gas-tight immobilization of the sensing element to be attained efficiently.

[0004] The features set forth in the dependent claims make possible developments of and improvements to the sensor according to the invention and the method for its manufacture. A particularly mechanically stable and gas-tight join between the sensing element and the ceramic shaped elements is achieved if the glass seal covers the sensing element over as large an area as possible, but does not penetrate appreciably into the front region which is subject to high thermal stress when the sensor is later operated. The arrangement of a powdered additional seal on the measured-gas site in front of the glass seal prevents the molten glass from penetrating, during the melting process, into the front region of the sensing element that is subject to high thermal stress. It is advantageous for the manufacturing process that the two ceramic shaped elements are configured, on the end faces which face toward one another, in the form of a die and punch, and act accordingly on one another. This makes possible compression of the glass seal, and of the powdered additional seal that is optionally used, utilizing the geometry of the ceramic shaped elements. The presence of a gap between die and punch has the advantage that the glass seal can escape into the gap upon compression. This makes it possible to work with a high compressive force. At the same time, it prevents the two end faces of the ceramic shaped elements from striking one another. In addition, a further glass seal can be inserted into the annular gap between the ceramic shaped elements, or an annular metal foil or plate can be set in place, thus resulting in a positive join between the two ceramic elements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Three exemplary embodiments of the invention are depicted in the drawings and explained in more detail in the description below. In the drawings:

[0006]FIG. 1 shows a sectioned depiction through a sensor according to the invention;

[0007]FIG. 2 shows a first exemplary embodiment of a sensing element seal for the sensing element in the uninstalled state, with an apparatus for manufacturing the seal;

[0008]FIG. 3 shows a second exemplary embodiment of a sensing element seal in the uninstalled state; and

[0009]FIG. 4 shows a third exemplary embodiment of a sensing element seal in the uninstalled state.

DETAILED DESCRIPTION

[0010] The sensor depicted in FIG. 1 is an electrochemical sensor for determining the oxygen content in exhaust gases of internal combustion engines. The sensor has a metal housing 10 in which a flat-plate sensing element 12, having a measured-gas-side end section 13 and a connector-side end section 14, is arranged. Housing 10 is configured with threads as attachment means for installation into an exhaust pipe (not depicted). Also arranged in housing 10 is a longitudinal bore 16 having, for example, a first shoulder-like annular surface 17 and a second shoulder-like annular surface 18.

[0011] Arranged in longitudinal bore 16 is a measured-gas-side ceramic shaped element 20 having a measured-gas-side passthrough 24, and having a measured-gas-side end face 21 and a connector-side end face 22. Measured-gas-side end face 21 is configured with a conically extending sealing seat 23 which sits on a metal sealing ring 25 that rests against second shoulder-like annular surface 18. Arranged above measured-gas-side ceramic shaped element 20 is a connector-side ceramic shaped element 27 having a connector-side passthrough 30 and having a measured-gas-side end face 28 and a connector-side end face 29.

[0012] A disk spring 31 that is under mechanical preload, which presses via a tubular retaining cap 32 onto measured-gas-side ceramic shaped element 27 that projects out of housing 10, rests on connector-side end face 29 of connector-side ceramic shaped element 27; retaining cap 32 engages via snap-lock tabs 34 into an annular groove 33 arranged on the outer side of housing 10. The two ceramic shaped elements 20, 27 are preloaded in the axial direction via retaining cap 32 and disk spring 31, so that measured-gas-side ceramic shaped element 20 presses with conical sealing seat 23 onto sealing ring 25. A gas-tight sealing seat thus forms between housing 10 and ceramic shaped element 20.

[0013] Measured-gas-side end section 13 projecting out of the housing is, for example, surrounded at a distance by a double-walled protective tube 37 having gas inlet and gas outlet openings 38. On connector-side end section 14, sensing element 12 has contacts (not depicted further) which make contact with connector cables 42 via a contact plug 41. Connector plug 41 includes, for example, two ceramic elements which are held together by a clamping piece 43. Connector-side end section 14 of sensing element 12, which projects out of connector-side ceramic shaped element 27, is surrounded by a metal sleeve 45 which is welded in gas-tight fashion to housing 10 and has a tubular opening 47 in which a cable passthrough 48 is located for the passage of connector cable 42.

[0014] Measured-gas-side ceramic shaped element 20 has on connector-side end face 22 a punch-shaped extension 51 which surrounds measured-gas-side passthrough 24. Connector-side ceramic shaped element 27 has on measured-gas-side end face 28 a recess 52 into which punch-shaped extension 51 penetrates with a radial gap 53. A cavity 55, which is filled with a glass seal 57, is formed between the end face of punch-shaped extension 51 and the bottom of recess 53. It is also possible to configure punch-shaped extension 51 on connector-side ceramic shaped element 27, and recess 52 on measured-gas-side ceramic shaped element 20.

[0015] Glass seal 57 causes sensing element 16 to be hermetically sealed in ceramic shaped elements 20, 27. The dimensions of punch-shaped extension 51 and of recess 52 are such that an annular gap 59 is formed between the mutually facing annular surfaces of measured-gas-side ceramic shaped element 20 and connector-side ceramic shaped element 27. The purpose of annular gap 59 is to allow the fusible glass of glass seal 57 to escape via radial gap 53 into annular gap 59 upon compression.

[0016] A fusible glass, for example a lithium aluminum silicate glass or a lithium barium aluminum silicate glass, is suitable as glass seal 57. Additives which improve the flow characteristics of the molten glass can be added to the fusible glass.

[0017] Powdered substances such as copper, aluminum, iron, brass, graphite, boron nitride, MoS₂, or a mixture of these substances, can be used as additives for plastification of glass seal 57 during the joining process. Lithium carbonate, lithium soap, borax, or boric acid are used, for example, as fluxes for glass seal 57. The addition of compensating fillers, such as aluminum nitride, silicon nitride, zirconium tungstate, or a mixture of these substances, is suitable for adjusting the thermal expansion. A further improvement in the join between glass seal 57 and the ceramic of ceramic shaped elements 20, 27 is achieved if a ceramic binder, such as aluminum phosphate or chromium phosphate, is added to glass seal 57.

[0018] In order to achieve large-area wetting of sensing element 12 with glass seal 57, in the present exemplary embodiments the side surfaces of measured-gas-side passthrough 24 and of connector-side passthrough 30 of ceramic shaped elements 20, 27 are each configured, toward cavity 55, with a conically extending enlargement 61 (FIGS. 2, 3, and 4).

[0019] Three exemplary embodiments of the sensing element seal in the uninstalled state, in each case with an apparatus for manufacturing glass seal 57, are evident from FIGS. 2, 3, and 4.

[0020] The apparatus has a support 70 acting as die, with a receptacle 71 and a stop 72. Ceramic shaped elements 20 and 27 are positioned in receptacle 71 with sensing element 12 received in passthroughs 24, 30. The axial position of sensing element 12 is defined in this context by stop 72, sensing element 12 resting with measured-gas-side end section 13 on stop 72. Measured-gas-side ceramic shaped element 20 is first inserted with sensing element 12 into receptacle 71. A glass blank 63, for example in the form of a glass pellet or glass film, is placed onto the end surface of punch-shaped extension 51, glass blank 63 having an opening with which glass blank 63 is slid over sensing element 12. Connector-side ceramic shaped element 27 is then placed onto glass blank 63, so that connector-side end section 14 of sensing element 12 projects through passthrough 30. In the arrangement described, a compressive force of, for example, 600 kg-force is applied onto connector-side ceramic shaped element 27 using a pressing punch 74. Beforehand, however, glass blank 63 was heated, for example by a heating device housed in support 70, to a temperature above the softening temperature of the fusible glass or glass ceramic being used. Upon compression, the fluid glass blank 63 deforms and is thereby pressed into conical enlargements 61 and into radial gap 53. Fusible glass flowing out via radial gap 53 can escape into end-surface annular gap 53.

[0021] A second exemplary embodiment is depicted in FIG. 3. This exemplary embodiment differs from the exemplary embodiment of FIG. 1 in that a further annular glass blank 64 is inserted into annular gap 59. Upon compression, the fluid further glass blank 64, like glass blank 63, deforms so that annular gap 59 is additionally sealed with a further glass seal.

[0022] A further exemplary embodiment of a sensing element seal is evident from the arrangement in FIG. 4. Here a further blank 65, precompressed and optionally presintered, is arranged on the measured-gas side below glass blank 63. Materials with good plastic deformability, such as talc, kaolin, clay, bentonite, graphite, boron nitride, etc. are in principle particularly suitable as the material for further blank 65. As punch 74 is applied during compression of the fluid glass blank 63, blank 65 is simultaneously deformed into its powder constituents, thus resulting in a powdered additional seal. Before the fusible glass flows in, the powder penetrates into the gap of measured-gas-side passthrough 24 formed by conical enlargement 61, so that the fusible glass is prevented from flowing to the measured-gas end of ceramic shaped element 20 that is subject to high thermal stress.

[0023] The apparatuses depicted in FIGS. 3 and 4 correspond to the apparatus of FIG. 2. The method for manufacturing glass seal 57 according to FIG. 4 can be carried out in accordance with the method implemented using the apparatus in FIG. 2. It is also possible, however, first to deform further blank 65 into powder using a punch and press it into the gap between sensing element and measured-gas-side passthrough, and then to compress glass blank 63 using the procedure according to FIG. 2. A further embodiment of the sensing element seal according to FIG. 4, having a further fused glass seal in annular gap 59 as in the case of the exemplary embodiment in FIG. 3, is also possible. 

1. A sensor, in particular for determining the oxygen content in exhaust gases of internal combustion engines, having a receptacle, arranged in a longitudinal bore of a metal housing, for a sensing element, in which receptacle the sensing element is received in gas-tight fashion via a sensing element seal, the sensing element seal containing a glass seal, wherein the receptacle for the sensing element (12) has a measured-gas-side ceramic shaped element (20) and a connector-side ceramic shaped element (27); and a cavity (55) into which the glass seal (57) is pressed while hot is configured between the two ceramic shaped elements (20, 27).
 2. The sensor as defined in claim 1 , wherein the measured-gas-side ceramic shaped element (20) and the connector-side ceramic shaped element (27) are arranged axially one behind another; the one ceramic shaped element (20) has a punch-shaped extension (51) and the other ceramic shaped element (27) has a recess (52); and the cavity (55) is configured in the recess (52).
 3. The sensor as defined in claim 2 , wherein the punch-shaped extension (51) is configured on the measured-gas-side ceramic shaped element (20), and the recess (52) on the connector-side ceramic shaped element (27).
 4. The sensor as defined in claim 2 or 3 , wherein the punch-shaped extension (51) in the recess is surrounded by a radial gap (53).
 5. The sensor as defined in claim 1 , wherein the glass seal (57) contains a lithium aluminum silicate glass or a lithium barium aluminum silicate glass.
 6. The sensor as defined in claim 1 or 5 , wherein the glass seal (57) contains, in addition to the glass constituents, additives such as plasticizers, fluxing agents, fillers, or a mixture of these additives.
 7. The sensor as defined in claim 6 , wherein the plasticizers are substances such as copper, aluminum, iron, brass, graphite, boron nitride, MoS₂, or a mixture of these substances.
 8. The sensor as defined in claim 1 , wherein the ceramic shaped elements (20, 27) each have an axially extending passthrough (24, 30) for receiving the sensing element (12); and at least one of the passthroughs (24, 30) of the ceramic shaped elements (20, 27) is configured with an expansion (61) facing the cavity (55).
 9. The sensor as defined in claim 1 , wherein at least on the measured-gas-side ceramic shaped element (20), the sensing element seal has, in addition to the glass seal (57), at least one powdered sealing packing.
 10. The sensor as defined in claim 9 , wherein the powdered sealing packing is arranged in the cavity (55), adjacent to the glass seal (57), on the side subject to greater thermal stress.
 11. The sensor as defined in claim 10 , wherein the powdered sealing packing is made of a ceramic.
 12. The sensor as defined in claim 9 , 10 , or 11, wherein the powdered sealing packing is made of steatite, graphite, boron nitride, Al₂O₃, ZrO₂, or a mixture of these substances.
 13. A method for manufacturing a sensor as defined in one of claims 1 through 12, wherein a glass blank is inserted between the two ceramic shaped elements; and the glass blank is hot-pressed to form the glass seal at a temperature which corresponds at least to the softening temperature of the glass or glass ceramic that is used.
 14. The method as defined in claim 12 , wherein the compressive force for pressing the glass blank (63) is 400 to 700 kilogram-force.
 15. The method as defined in claim 12 or 13 , wherein the measured-gas-side ceramic shaped element, the sensing element, the glass blank, the connector-side ceramic shaped element, and optionally the powdered sealing packing are inserted in the assembled position into a die; the glass blank is heated in the die to at least the softening temperature; and the compressive force is then applied onto the connector-side ceramic shaped element using a punch. 